linux-kernel - Re: [PATCH 1/2] tpm, tpm_tis: Handle interrupt storm

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Message-ID: <20230523074443.GA21236@wunner.de>
Date:   Tue, 23 May 2023 09:44:43 +0200
From:   Lukas Wunner <lukas@...ner.de>
To:     Péter Ujfalusi <peter.ujfalusi@...ux.intel.com>
Cc:     Lino Sanfilippo <LinoSanfilippo@....de>, peterhuewe@....de,
        jarkko@...nel.org, jgg@...pe.ca, jsnitsel@...hat.com,
        hdegoede@...hat.com, oe-lkp@...ts.linux.dev, lkp@...el.com,
        peterz@...radead.org, linux@...ewoehner.de,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        l.sanfilippo@...bus.com, p.rosenberger@...bus.com
Subject: Re: [PATCH 1/2] tpm, tpm_tis: Handle interrupt storm

On Tue, May 23, 2023 at 09:48:23AM +0300, Péter Ujfalusi wrote:
> On 22/05/2023 17:31, Lino Sanfilippo wrote:
[...]
> This looked promising, however it looks like the UPX-i11 needs the DMI
> quirk.

Why is that?  Is there a fundamental problem with the patch or is it
a specific issue with that device?


> > --- a/drivers/char/tpm/tpm_tis_core.c
> > +++ b/drivers/char/tpm/tpm_tis_core.c
> > @@ -752,6 +752,55 @@ static bool tpm_tis_req_canceled(struct tpm_chip *chip, u8 status)
> >  	return status == TPM_STS_COMMAND_READY;
> >  }
> >  
> > +static void tpm_tis_handle_irq_storm(struct tpm_chip *chip)
> > +{
> > +	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
> > +	int intmask = 0;
> > +
> > +	dev_err(&chip->dev, HW_ERR
> > +		"TPM interrupt storm detected, polling instead\n");
> 
> Should this be dev_warn or even dev_info level?

The corresponding message emitted in tpm_tis_core_init() for
an interrupt that's *never* asserted uses dev_err(), so using
dev_err() here as well serves consistency:

	dev_err(&chip->dev, FW_BUG
		"TPM interrupt not working, polling instead\n");

That way the same severity is used both for the never asserted and
the never deasserted interrupt case.


> > +	if (priv->unhandled_irqs > MAX_UNHANDLED_IRQS)
> > +		tpm_tis_handle_irq_storm(chip);
> 
> Will the kernel step in and disbale the IRQ before we would have
> detected the storm?

No.  The detection of spurious interrupts in note_interrupt()
hinges on handlers returning IRQ_NONE.  And this patch makes
tis_int_handler() always return IRQ_HANDLED, thus pretending
success to genirq code.


> >  	rc = tpm_tis_write32(priv, TPM_INT_STATUS(priv->locality), interrupt);
> >  	tpm_tis_relinquish_locality(chip, 0);
> >  	if (rc < 0)
> > -		return IRQ_NONE;
> > +		goto unhandled;
> 
> This is more like an error than just unhandled IRQ. Yes, it was ignored,
> probably because it is common?

The interrupt may be shared and then it's not an error.

Thanks,

Lukas